Insulinomas are rare neuroendocrine tumours that classically present with a combination of symptomatic hypoglycaemia, low serum glucose values and resolution of symptoms post glucose ingestion.
We describe a 65-year-old lady who repeatedly presented over several years with recurrent infections, predominantly of the urinary tract, nausea and diarrhoea, necessitating frequent hospital admissions. Despite extensive investigations, no clear cause for her symptoms was identified. These ongoing episodes were incidentally noted to occur with clinical and biochemical hypoglycaemia (serum glucose values even as low as 1.7 mmol/l), seen to correct by administering intravenous dextrose. She was subsequently, referred to her local Endocrinologist. 0900 h Cortisol and short synacthen test were normal. A 72 h fast was unfortunately terminated prematurely due to severe symptomatic hypoglycaemia (serum glucose of 2.8 mmol/l). A raised C-Peptide of 798 pmol/l and Insulin of 8.2 (3-17 μ/l) with a negative sulphonylurea screen, at the time of hypoglycaemia, biochemically confirmed inappropriate endogenous insulin secretion, as seen with insulinomas.
Magnetic resonance imaging could not exclude a small insulinoma. She declined all further investigations, hence Diazoxide was commenced and although the frequency of hypoglycaemia reduced markedly, her nausea worsened. Diazoxide was, therefore, replaced by twice daily injections of short-acting octreotide, which achieved glycaemic control and she reported some improvement of her nausea. It was then decided to trial Lanreotide, which has successfully controlled both her hypoglycaemia and nausea, consequently reducing hospital admissions and allowing our patient to regain a decent quality of life.
Diagnosis of insulinomas is usually dependent upon clinical presentation, confirmation of hyperinsulinism and diagnostic imaging. This was a difficult case where the clinical suspicion of insulinoma was confirmed following initiation of medication to suppress insulin release.
Although rare, it is paramount that insulinomas are considered in patients with unexplained hypoglycaemia.